1. Field of the Invention
This invention relates generally to lighting assemblies for projecting a beam of light and more particularly to a system having a reflector and a light source wherein the source of light is optimally placed with reference to the reflector.
2. Description of the Related Art
Ellipsoidal spotlights have been used for a number of years in the theatrical industry. An example of such a spotlight is described in U.S. Pat. Nos. 5,345,371 and 5,446,637. These particular theatrical ellipsoidal spotlights have a near-elliptical reflector and an incandescent lamp that has four linear, helically wound coil filaments that are spaced around the central longitudinal axis of the lamp and extend parallel to the central axis of the lamp. The lamp, in turn is positioned through a coaxial aperture in the rear of the reflector so that the lamp axis and the reflector axis coincide. The lamp is so designed that when the lamp is fully inserted and secured in place the filaments are located in a spaced relation around the focal point of the reflector. Such an arrangement is described in U.S. Pat. No. 5,268,613, issued to Cunningham. This patent teaches that for optimum illumination of the target, utilizing an ellipsoidal or parabolic reflector and an incandescent lamp, the filament should be coincident with the rough focal point of the reflector. Further, the filament axial length should be as short as possible in order to maximize light impingement on the reflector such that it is reflected through the spotlight's aperture. Further, the filaments should extend parallel to the central axis of the reflector with their centers as close to the focal point as possible. To that end, the Cunningham apparatus, one embodiment of which is commercially known as an ETC Source 4 lighting assembly, includes an adjustable feature to axially adjust the position of the incandescent bulb within a millimeter or two about the focal point to correct for manufacturing tolerances in axial placement of the filaments within the replaceable bulb. However, the placement of a filament directly on the central axis with its center at the focal point, is discouraged as counterproductive in that its light would be absorbed by the filaments spaced from the central axis. Further, the adjustability feature falls short of being capable of positioning the filaments in this prior-art bulb at the optimum axial location as discussed below with reference to the present invention.
The purpose of utilizing a reflector with a light source is to project a beam of light in a given direction, usually along the central axis, of the reflector. It is also desirable to project as much light as possible for a given power input to the light system. Consequently there is a continuing need for improved illumination and light projection from a given lighting fixture design.